The objective of the study is to evaluate thrombolytic therapy using recombinant tissue plasminogen activator (rtPA) for treatment of acute deep vein thrombosis (DVT) of the lower extremity. While the conventional therapy, anticoagulation alone, is highly effective in prevention of life threatening pulmonary embolism, it does not preserve venous function in the affected leg, often leading to postphlebitic syndromes in subsequent years. The study is designed to evaluate efficacy, safety, and cost of this form of treatment for restoration of venous function in the lower extremity.This spting,we have completed treatment of 20 patientsas as was alotted for this pilot study . All except one patient had significant improvement. Five patients also had evidence of pulmonary embolism by lung scans prior to start of their treatment whereas only two patients have had evidence of small asymptomatic pulmonary emboli that developed during treatment, detected on ventilation perfusion lung scans that are obtained in all patients accepted into the protocol. None of these patients were clinically symptomatic. One patient developed a non-life-threatening biceps hematoma probably induced by automatic blood pressure monitoring during the rtPA treatment. No patients have required blood transfusions and no other complications have occurred. Over a followup period that ranges from 1 month to 5 years, none of our patients have developed either recurrent deep vein thrombosis or progression to postphlebitic syndromes.Pharmacokinetic studies in our patients have made major contributions to improving our understanding of thrombolytic therapy and has led us to design and open a new protocol (04-CC-0178;Principal investigator:Dr Horne)for DVT of the lower extremity using substantially lower doses of tPA that theoretically should be an even sa